1. Field of the Invention
This invention relates to feed systems for imparting scanning motion to an antenna, and more particularly to such a feed system for use in an antenna having a focus device, such as a reflector.
2. Description of the Prior Art
There is a need for passive angle tracking to be performed using the antenna of an active conical scan radar. Typically this need arises from a requirement to provide passive angle tracking of external emitters associated with the target being tracked, as in the case of electronic counter measures (E.C.M.) equipment or electronic counter-counter measures (E.C.C.M.) equipment.
One prior approach involves internal modification of the wave guide system of the radar in order to pass the received information to the passive receiver. The disadvantages of this approach include the fact that the sensitivity of both the passive receiver and the tracking radar are diminished, and that the bandwidth of the passive receiver is limited by the r.f. bandwidth of the radar system wave guide.
Included in the common methods of making tracking antennas are beam nutation, beam switching, and beam comparison. These methods use moving feeds, moving antennas, switched or phase shifted feeds or multiple components to derive relative "target" location by means of signal strength versus sense of direction in the appropriate system components. The difficulty in applying these approaches in fulfilling a need for such secondary passive angle tracking antenna, is that they are limited in bandwidth. The function of passive angle tracking of external emitter radiations requires broad bandwidths, namely a bandwidth which is multiple octaves of frequency in width.
Of course, it is also desirable that apparatus for passive angle tracking be inexpensive, easy to manufacture, and easy to install in existing active, conical scan radars.